The UK aviation regulator is being urged to act against Ryanair “rip-off” dynamic currency conversion fares.

Consumer group Which? Travel claims the no-frills carrier’s fares are inflated by 6% on average when rates are advertised in euros for flights from eurozone countries to the UK.

In one instance a family of four faced being charged an extra £30 by paying for their flight using Ryanair’s dynamic currency conversion.

Customers are faced with this system when Ryanair displays the price of a ticket in the currency of the departure airport, so if a passenger is buying a flight from France or Italy back to the UK, the fare is advertised in euros.

However, when prompting the customer to enter card details at the  end of the booking process, it switches the price into pounds – automatically applying an exchange rate.

Only after clicking ‘more information’ do customers find the option to opt out of paying in pounds and revert to euros. Ryanair warns that opting out could end up costing “significantly more”.

Which? is calling on the Civil Aviation Authority to single out Ryanair’s currency conversion tactic as part of a report expected to criticise airlines for failing to clearly spell out the true price of travel at the end of the month.

The authority must clamp down on the practice so that the airline is not able to continue “ripping-off” customers in this way, the consumer champion added.

Which? previously reported Ryanair’s use of dynamic currency conversion to the CAA, and this is the third time it has found the airline automatically opting in passengers to its currency conversion rates.

The carrier is now being accused by Which? of using misleading tactics which could be in breach of consumer protection legislation, specifically due to the opaque way it presents the rate to customers.

Which? advocacy director Caroline Normand said: “This cynical and misleading pricing trick is one of the clearest examples of a rip-off we have seen – but Ryanair has been allowed to get away with it due to a lack of action from the Civil Aviation Authority.

“If the regulator is committed to helping improve the experience of passengers, it must clamp down on this practice before thousands more holidaymakers are caught out this summer.”

Ryanair said: “Ryanair’s currency conversion presentation is fully transparent and complies with all applicable EU and national laws on consumer protection.

“Customers have the option of paying in the currency of their payment card which gives absolute certainty of the final payment amount.”